Steiner, George. Heidegger. Fontana Modern Masters, ed. Frank Kermode. London: Fontana Press, 1987. First published 1978.
Some quotes from it:
"It means ... that nothing very confident can be argued with regard to at least two of the most vexed topics in the whole study of Heidegger's accomplishment: the debate on whether or not there occurs a fundamental change or 'turn' (Kehre) between the author of Being and Time and the later Heidegger ... and the even sharper controversies on Heidegger's implication in Nazism." (10)
The passage that you might be interested is this: "Only conjecture is possible. Allegations of anti-semitism are, in respect of the magnitude of the case, trivial, but also, I believe false. I have been unable to locate anti-Jewish sentiments or utterances in the works of Heidegger, even in those of a public and political nature - a fact which, from the outset, isolates him from the mainstream of Nazism. If Heidegger was, on certain obvious levels, a great man, a teacher whose philosophic-linguistic activity literally towers over various aspects of contemporary speculation, he was, at the same time, also a small man. He led his existence amid a worshiping coterie and, particularly in his later years, behind barriers of adulation. His sorties into the world at large were few and carefully orchestrated. It may well be that he did not have the courage or magnanimity needed to confront his own political past, and the question of Germany's espousal of barbarism." (119)
On google books, a different edition is available.... the above page 119 appears on page 124: https://books.google.co.
in/books?id=BXnOkUp2D6EC& printsec=frontcover&dq=george+ steiner,+Heidegger&hl=it&sa=X& redir_esc=y#v=onepage&q= nazism&f=false.